162 UNIVERSITY OF COLORADO STUDIES 
Famity Lamnide (The Mackerel Sharks) 
Corax jalcatus Agassiz, is recorded from the Cretaceous of Colorado, and also occurs 
in Europe. I have collected teeth of this group near Las Vegas, New Mexico, and Colorado 
Springs, Colorado, but they were not determined. 
OrpvER BATOIDEI (The Rays) 
Famity Ptychodontide 
Ptychodus whipplei Marcou, occurs in the Niobrara Cretaceous of Colorado and 
New Mexico. I have collected the characteristic teeth near Las Vegas, N. M. 
Famity Dasyatide (The Sting Rays) 
Dasyatis radians Marsh. (Xiphotrygon acutidens Cope), is found in the Green River 
beds of Wyoming. 
SuscLtass HOLOCEPHALI (The Chimeras) 
In this group the skeleton is cartilaginous, and the skin is without scales. 
OrpvER CHIMERIOIDEI 
Famity Chimeride 
Some fossil genera referred here are of very doubtful affinities. Dictyorhabdus priscus 
Walcott, is from the Silurian or Ordovician of Colorado. Myledaphus bipartitus Cope, 
and Hedronchus sternbergi Cope, are from the Fort Union Cretaceous of Montana. With 
regard to the M yledaphus, Hatcher remarks that it was founded on isolated teeth, so unchar- 
acteristic as to be of little value for determining genera or species. Such teeth, however, 
are abundant in the Judith River beds and the Laramie. Hedronchus was based on part 
of a tooth. The modern Chimeride are found in the seas of cold regions (Jordan and 
Evermann). 
SuspcLass TELEOSTOMI (The True Fishes) 
OrDER SIRENOIDEI 
Famity Ceratodontide 
The genus Ceratodus Agassiz, is represented by five fossil species. From the Jurassic 
are C. americanus Knight (Wyoming), C. guentheri Marsh (Colorado), and C. robustus, 
Knight (Wyoming). From the Cretaceous, C. eruciferus Cope and C. hieroglyphus Cope; 
according to Hatcher these latter occur in the Judith River beds of Montana. 
OrpER RHIPIDISTIA 
FamiLy Holoptychiide 
Eriptychius americanus Walcott, 1892, is from the Lower Silurian or Ordovician of 
Colorado. 
OrpER SELACHOSTOMI 
Famity Polyodontidze (The Paddle Fishes) 
Crossopholis magnicaudatus Cope, comes from the Eocene of Wyoming. 
OrDER CHONDROSTEI (The Sturgeons)! 
Famity Acipenseride 
Length up to five feet; snout broad and depressed, subspatulate (Missouri R. at Fort 
Benton, Mont., Henshall) . . . . . . Scaphirhynchus platorynchus (Raf.) 
(Shovel-nose Sturgeon). 
t Diphyodus longirostris Lambe, is based on fragmentary jaws of uncertain affinities, from the Cretaceous 
of Canada, and also occurring in Montana and Wyoming. 
